I know all about PS3MC, a bunch of friends have been working on it for ages, but I know little to nothing about Natal aside from the video today. But if it can detect where limbs are and depth as well, then it should be adaptable to all types of games including fps. In other words, if it can position your hands in three space, then you should be able to do just about anything with it. It may be dependent on software support for that, but that's Microsoft strong suit anyways.
Not to mention that Natal doesn't need to replace existing controllers and be the only one, unlike the glowstick solution.
Other peripherals can be held in the hands for games that need it.
Consider other possible solutions, like head tracking (turn your head to turn the camera in a FPS) while holding a traditional 360 controller. Or have another kind of game where the player stands up using the controller and could use their legs to control something (eg, a football).